1. Field of the Invention
The present invention relates to an aqueous coating composition and a floor polishing composition using the aqueous coating composition.
2. Description of the Background Art
A beautiful outward appearance is required for floor materials in department stores and convenience stores. Because these floor materials are severely contacted by customer""s shoes (especially, by women""s high-heeled shoes), the coating agent or polishing agent for the floor materials must have high durability.
As a coating agent with excellent durability, Japanese Patent Application Laid-open No. 225670/1988, for example, discloses a UV curable resin composition which comprises a photopolymerizable prepolymer containing a carboxylic acid group and/or a carboxylate group and a photoinitiator.
Because the photopolymerizable prepolymer disclosed in this patent application is polymerizable by itself, the photopolymerizable prepolymer crosslinks by irradiation with UV light and forms a strong film. Therefore, a coating agent containing such a composition has reduced alkali solubility and thermoplasticity.
The reduced alkali solubility and thermoplasticity impair delamination properties of the coatings with alkali and dry buff applicability when the coating agent is used for polishing floors.
An object of the present invention is to provide an aqueous coating composition and a floor polishing composition exhibiting excellent delamination properties and dry buff applicability.
The aqueous coating composition of the present invention comprises:
(A) 100 parts by weight (on a solid component basis) of an aqueous dispersion of a copolymer obtained by the emulsion polymerization of (a) 5-30 wt % of an ethylenically unsaturated carboxylic acid monomer, (b) 10-80 wt % of a (meth)acrylic acid alkyl ester monomer, and (c) 0-85 wt % of a monomer polymerizable with the monomers (a) and (b), provided that the total of monomers (a), (b), and (c) is 100 wt %,
(B) 0.5-200 parts by weight of an unsaturated monomer curable with energy rays, and
(C) a photoinitiator in an amount of 0.01-10 parts by weight for 100 parts by weight of the component (B).
The aqueous coating composition of the present invention can produce coatings exhibiting excellent solubility in alkali, thermoplasticity, and durability. The reason is considered to be as follows.
The aqueous coating composition of the present invention contains (A) a copolymer made form ethylenically unsaturated monomers and (B) energy ray curable unsaturated monomer. Therefore, if the aqueous coating composition is irradiated with an energy ray, for example, ultraviolet radiation, the energy ray curable unsaturated monomer polymerizes producing a polymer or copolymer (hereinafter referred to as xe2x80x9c(co)polymerxe2x80x9d). Specifically, both the copolymer (A) containing ethylenically unsaturated monomers and the copolymer containing the energy ray curable unsaturated monomers (B) are present in the coating agent containing this aqueous coating composition. For this reason, the coating agent containing the aqueous coating composition of the present invention is more soluble in alkali and exhibits better thermoplasticity than the above-described polymers made from photopolymerization property prepolymers. In addition, due to inclusion of the (co)polymer made from energy ray curable unsaturated monomers (B), the aqueous coating composition of the present invention has durability which is more excellent than that of copolymers made only from ethylenically unsaturated monomers.
The copolymer used in the aqueous coating composition of the present invention preferably has a weight average molecular weight of 200,000 or more.
The content of components insoluble in solvents in the copolymer is 20-98 wt %. The solvent here is toluene.
The aqueous coating composition of the present invention can be used as a floor polishing composition.
Other objects, features and advantages of the invention will hereinafter become more readily apparent from the following description.